Combustion grate and process for optimizing its operation

ABSTRACT

A combustion grate including fire bars which are either wholly or partially cooled by a fluid circulating in a closed regulating circuit. The flow lines which conduct the fluid have thermal expansion capability. In particular, windings are provided in the shape of a helical spring in these flow lines. The fire bars include corrugated exchangers and can be replaceable rods.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of Swiss application 830/95-6 andPCT/CH96/00092, the disclosures of which are expressly incorporated byreference herein.

The present invention relates to a combustion grate as well as to amethod for optimizing the operation of a combustion grate.

It is known that combustion chambers can be used preferably for burningvarious fuels, such as household waste, industrial waste, wood waste,solid, porous, and liquid fuels as well as fuels with high and lowignition performance. Such known combustion chambers are typicallycomposed of a mechanical grate and by cooled or uncooled fireproof sidewalls.

Systems of this kind have the disadvantage that their operation are notoptimal for all fuels, and therefore certain parts of such systems,especially parts of the grate, suffer from defects and short servicelives.

Systems for cooling grate coatings are already known such as cooling thegrate surface by using the combustion air flowing past in the air hornsor forced cooling of the grate surface by the combustion air, which isforced through a chamber formed by the fire bar and a conducting panel,into the combustion chamber.

These known types of cooling systems depend upon the volume ofcombustion air, and the air outlets in the combustion chamber can beclogged by ashes, solid metals, or slag. As a result, the cooling of therespective surface is no longer ensured. This can lead to problems. Atthe same time, these types of cooling systems suffer from thedisadvantage that the volume of combustion air has a function that isrelated primarily to the technology of the process and is not requiredto perform a cooling function. Changing the volume of combustion air asa function of the cooling effect is not always feasible. In this casealso, the cooling effect of the grate surface is not ensured.

Water cooling for the grate surface is also known. The volume of waterintended for cooling the grate surface keeps the grate surface at anapproximately constant temperature, independently of the heating valueof the fuel. Once again, this is disadvantageous when burning fuels witha low heating value because the combustion chamber loses heat. In thiscase, a higher cast-surface temperature would be advantageous forcombustion.

DE-U-93 09 198 discloses a combustion grate in which a liquid or gaseousmedium can be conducted through the fire bars to control theirtemperature. Depending on the requirement, the grate can either becooled or heated. The grate in this case has the general form of aboard, in other words a largely plane external surface. Within thegrate, baffles can be provided to form a labyrinth for thetemperature-controlling medium.

It has been found, however, that problems regarding the expansion of thetempering medium occur as a result of the very high temperaturefluctuations that occur, especially when a large number of fire bars areto have their temperatures controlled at the same time.

An object of the present invention is to provide an improved combustiongrate and method to remedy this disadvantage and to ensure reliabletemperature control to optimize fuel combustion.

To this end, the combustion grate according to the present invention andthe method for its optimum operation utilize whole or partial cooling byboth gas and fluid via a regulating circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawingswherein:

FIG. 1 is a cooling schematic view for an air/water-cooled combustiongrate with a closed regulating circuit;

FIG. 2 is a side view of a feed grate;

FIG. 3 is a view similar to FIG. 2 of a grate zone on an enlarged scale;

FIG. 4 is a sectional view along section line IV—IV of FIG. 3;

FIG. 5 is a perspective view of an air/water-cooled fire bar in a sideview from the front, with parts cut away;

FIG. 6 is a perspective view of the air/water-cooled fire bar of FIG. 5but in a side and rear view; and

FIG. 7 is a rotating fire bar with side wall removed and metal hoseconnecting lines.

DETAILED DESCRIPTION OF THE DRAWINGS

The air/water-cooled combustion grate in FIGS. 1 to 7 is configured as afeed grate as far as its function is concerned. However, the presentinvention can be used as easily for other grate designs, such as apyrolysis grate, degassing grate, gasification grate, combustion grate,high-temperature combustion grate, cooling grate, transport grate,countercurrent grate, opposing-feed grate, reversed-feed grate, rollergrate, and the like.

The feed grate 1 shown schematically in FIG. 1 serves to transport thefuel and the slag that results from combustion through the combustionchamber and simultaneously to function as a combustion air distributiondevice.

The grate consists of a plurality of zones arranged horizontally or atan angle. The individual zones can lie on the same plane or be separatedby a drop.

Each individual grate zone consists of fixed and movable grate sectionswith fixed fire bars 3 and movable fire bars 2. The movable sections aremoved forward and backward with a variable number of strokes, causingthe fuel to be transported and consumed. The number of strokes dependson the fuel and the combustion process. Combustion takes place in thefuel layer, through which the combustion air, the so-called under-grateblast, is blown from below through gaps in grate surface 22 (FIG. 2)into the combustion chamber. The combustion air, which is effectivelyconnected by a heat exchanger with the regulating circuit,simultaneously serves to cool the grate surface 22. The gaps between theindividual fire bars 2 and 3 must be so small that as few unburned smallparticles fall through as possible. These gaps are all distributeduniformly over the entire grate surface.

The length of the strokes and the stroke speed of movable grate surface22 of individual grate zones 20 is adjusted as a function of the heatgenerated on grate 1 and/or in the combustion chamber.

Grate surface 22 conveys the fuel through the combustion chamber.

Grate surface 22 serves as an air distribution device for theunder-grate blast.

Grate surface 22 is subject to high thermal stress and, because of thehigh acquisition costs and long downtimes when repairs must be made,must have a long service life and high operating reliability.

The coolant for feed grate 1 is supplied through distributors 5, andafter flowing through fire bars 2 and 3 is collected and returned incollectors 6. Water can be used as the coolant, as can fluids with highboiling points, for example certain oils, in particular. It is alsopossible, however, to use the closed regulating system shown in FIG. 1to warm the coolant and thus cause it to give off heat to the grate asit flows through feed grate 1.

It is clear from the diagram of the cooling water in FIG. 1 that thiswater or the fluid flowing through the flow lines connected to the gratecan be cooled or heated in a heat exchanger.

Another heat exchanger in the water network serves to heat or cool theunder-grate blast. By mounting a temperature sensor or atemperature-measuring point, a desired temperature in the combustionchamber, especially the temperature of the under-grate blast, can bemeasured after it leaves grate 1. By appropriate regulation of the fluidmedium flowing through the grate, the temperature of the under-grateblast can be raised or lowered, depending on the regulating programprovided, which in particular must be adapted to the specific type offuel.

In this manner, considerable advantage is obtained in that thethrough-flow medium can be used to change the under-grate blasttemperature within the designated limits without the volume ofunder-grate blast being influenced thereby.

In the cooling water diagram shown in FIG. 1, the necessary through-flowfixtures are also provided to allow regulating parts to be bypassed andto disconnect them.

The flow of coolant is indicated by the corresponding arrows.

FIG. 2 shows a feed grate 1 with three grate zones 20. Fire bars 2, 3are mounted on grate carriages 21 and have a grate surface 22 that facesthe combustion chamber. Air horns 23 are provided on the underside offeed grate 1 and define air zones 24.

FIG. 3 shows on an enlarged scale a side view of a grate with fixedgrate stages 27 and movable grate stages 28. Line 30 is used to feed thecoolant into the fixed grate stages, while line 31 is used to feedcoolant into movable grate stages 28. FIG. 3 likewise shows a feedwatercylinder 33 which takes into account the displacements of movable gratestages 28.

In FIG. 4, the two lines 30, 31 are likewise visible. In addition, theoutflow lines 35, 36 for the through-flow medium are shown.

FIGS. 5 and 6 show, in a perspective view, details of a simplifiedconfiguration of an air/water-cooled fire bar. This can be a movablefire bar 2 or a fixed fire bar 3. This fire bar with grate surface 22has a partition 40 in its interior so that, looking in the lengthwisedirection, a first cooling chamber 41 and a second cooling chamber 42parallel thereto result. At the forward end of fire bar 2 or 3, there isa water through-flow opening 43. This opening constitutes the linkbetween the two cooling chambers 41, 42. In each of these coolingchambers, a corrugated exchanger or guide panel 45 is mounted parallelto partition 40 for improving the heat exchange.

Fire bars 2, 3 are pivotably mounted on a grate shaft 46. Immediatelybelow grate shaft 46, a distributor 48 supports grate shaft 46, andbelow the distributor, a collector 47, in combination with cooling watersupply line 50 and hot water return line 51, ensure the flow of thecoolant through the fire bar.

As a result of the considerable temperature differentials that appear inthe grate in the operating and nonoperating states, and as a result ofthe movements of fire bars 2, cooling water supply and return lines 50and 51 are provided with turns like those of a coil spring, i.e.so-called temperature or thermal expansion compensating elements 52.

As a result of this arrangement, the cooling system is kept tight at theconnections during both the resting and operating states.

FIG. 7 shows a rotating fire bar or replaceable rod 60 pivotably mountedon a fire bar support 61. Below this fire bar support 61, a supportingcoolant distributor 62 is combined with a collector 63. One coolingchamber 65 is equipped with a corrugated conducting panel 66. In thiscase, a connecting line 68 consisting of a metal hose is provided toensure connections for the through-flow medium that are free of thermalstress.

Since this is a so-called rotating fire bar 60, a bearing shell 70 islikewise provided at its forward end so that, in the event of nonuniformwear of grate surface 22, the rotating fire bar 60 is rotated andforward bearing shell 70 can be placed on fire bar support 61.Corresponding connections and links are provided at the forward end ofrotating fire bar 60, as can be seen.

With the system described and the regulating circuit provided, theair/water-cooled grate surface can be used to limit the influence ofthermal overloads on the combustion grate locally or over the entiregrate surface such that the known operating problems and wear of thegrate surface can be largely eliminated. This is due to the air/watercooling of the grate surface, as shown and explained in FIG. 1. Coolingtakes place as a function of the volume of cooling water and thetemperature of the cooling water as well as the release of heat on thegrate. For this purpose, as explained above, the temperature isregulated by a temperature sensor or a temperature-measuring system.

Another special feature of the invention consists in the fact that, whenburning waste with a low heating value, the heat which is drawn from theliquid circuit into the fire bar, as a result of very intensive heatexchange between the fire bar and the combustion air because of thegeometric shape of the fire bar, is given up to the combustion air.Thus, the combustion of the waste lying on the grate is accelerated.

When burning waste with a high heating value, a larger volume of heat isdrawn from the corresponding grate parts by the coolant, whereas whenburning waste with a low heating value, a lower heat value is carriedaway in the grate surface, which is used to warm up the combustion airto accelerate the combustion process in any case. The greater loss ofheat to the combustion air and thus the increase in air temperature isachieved by reducing the volume of cooling water to a greater degreebecause of the lower loss of specific heat released in the combustionchamber than to the grate, and thus the temperature of the cooling wateris increased to a greater degree. Consequently, an increased amount ofheat is given up by the fire bar to the combustion air.

In this fashion, as a result of cooling, advantages are obtained forburning waste with a high heating value as well as waste with a lowheating value, because the heat extracted from the combustion air can besupplied once again if necessary.

In this sense it is novel to separate the cooling function and themethod function in a logical fashion and thus create a situation inwhich, with a change in the volume of combustion air below the grate(under-grate blast) which is due to the technology employed in themethod, the effect of the cooling of the grate surface is influenced sothat for the most part no problems can occur.

What is claimed is:
 1. A combustion grate for transporting variousfuels, said grate comprising fire bars configured to be cooled by afluid medium, a regulating circuit and flow lines arranged to conductthe fluid medium, the flow lines being equipped with thermal expansioncompensators configured as windings having a helical spring shape. 2.The combustion grate according to claim 1, wherein the fire bars includecorrugated heat exchangers operatively connected with the flow lines. 3.The combustion grate according to claim 1, wherein the fire bars areconfigured as replaceable rods.
 4. The combustion grate according toclaim 3, wherein the fire bars include corrugated heat exchangersoperatively connected with the flow lines.
 5. The combustion grateaccording to claim 1, wherein the regulating circuit is a closedcircuit.
 6. The combustion grate according to claim 5, wherein the firebars include corrugated heat exchangers.
 7. The combustion grateaccording to claim 6, wherein the fire bars are configured asreplaceable rods.
 8. The combustion grate according to claim 1, whereinthe regulating circuit is configured to have control parameters thatinclude at least one of the through-flow volume of cooling fluid perunit time and the cooling fluid temperature.
 9. The combustion grateaccording to claim 8, wherein the fire bars include corrugated heatexchangers operatively connected with the flow lines.
 10. The combustiongrate according to claim 9, wherein the fire bars are configured asreplaceable rods.
 11. The combustion grate according to claim 10,wherein the regulating circuit is a closed circuit.
 12. The combustiongrate according to claim 1, wherein the regulating circuit comprises atleast one coolant heat exchanger and a combustion air heat exchanger.13. The combustion grate according to claim 12, wherein the fire barsinclude corrugated heat exchangers operatively connected with the flowlines.
 14. The combustion grate according to claim 13, wherein the firebars are configured as replaceable rods.
 15. The combustion grateaccording to claim 14, wherein the regulating circuit is a closedcircuit.
 16. The combustion grate according to claim 15, wherein theregulating circuit is configured to have control parameters that includeat least one of the through-flow volume of cooling fluid per unit timeand the cooling fluid temperature.
 17. The combustion grate according toclaim 1, wherein the regulating circuit includes a bypass.
 18. Thecombustion grate according to claim 17, wherein the fire bars includecorrugated heat exchangers.
 19. The combustion grate according to claim18, wherein the fire bars are configured as replaceable rods.
 20. Thecombustion grate according to claim 19, wherein the regulating circuitis a closed circuit.
 21. A combustion grate for transporting variousfuels, said grate being at least partially gas-cooled and liquid-cooledvia a regulating circuit, said grate further comprising grate bars andalso comprising pipes operatively connected with the grate bars, thepipes being configured for feeding and removal of liquid coolant to thegrate bars, the pipes also being equipped with thermal expansioncompensators configured as helical coil-spring-shaped windings.
 22. Thecombustion grate according to claim 21, wherein the grate bars includecorrugated heat exchangers.
 23. The combustion grate according to claim21, wherein the grate bars are replaceable rods.
 24. The combustiongrate according to claim 23, wherein the rods include corrugated heatexchangers.